De structuur van categorische input verkennen

In deze oefening roep je model.matrix() (docs) aan om te onderzoeken hoe R gegevens met zowel categorische als numerieke input voor modellering weergeeft. De gegevensset flowers (afkomstig uit het Sleuth3-pakket) is voor je ingeladen. Deze bevat de volgende kolommen:

Flowers: het gemiddelde aantal bloemen op een meadowfoam-plant
Intensity: de intensiteit van een lichtbehandeling die op de plant is toegepast
Time: een categorische variabele — wanneer (Late of Early) in de levenscyclus de lichtbehandeling plaatsvond

Het uiteindelijke doel is om Flowers te voorspellen als functie van Time en Intensity.

Deze oefening maakt deel uit van de cursus

Supervised Learning in R: Regressie

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Oefeninstructies

Roep de functie str() aan op flowers om de types van elke kolom te zien.
Gebruik de functie unique() op de kolom flowers$Time om de mogelijke waarden te zien die Time aanneemt. Hoeveel unieke waarden zijn er?
Maak een formule om Flowers uit te drukken als functie van Intensity en Time. Ken deze toe aan de variabele fmla en print hem.
Gebruik fmla en model.matrix() om de modelmatrix te maken voor het data frame flowers. Ken deze toe aan de variabele mmat.
Gebruik head() om de eerste 20 regels van flowers te bekijken.
Bekijk nu de eerste 20 regels van mmat.
- Is de numerieke kolom Intensity anders?
- Wat is er gebeurd met de categorische kolom Time uit flowers?
- Hoe wordt Time == 'Early' weergegeven? En Time == 'Late'?

Praktische interactieve oefening

Probeer deze oefening eens door deze voorbeeldcode in te vullen.

# Call str on flowers to see the types of each column
___

# Use unique() to see how many possible values Time takes
___

# Build and print a formula to express Flowers as a function of Intensity and Time: fmla
(fmla <- ___("Flowers ~ Intensity + Time"))

# Use fmla and model.matrix to see how the data is represented for modeling
mmat <- ___

# Examine the first 20 lines of flowers
___

# Examine the first 20 lines of mmat
___

Code bewerken en uitvoeren

Deze oefening maakt deel uit van de cursus

Supervised Learning in R: Regressie

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In this chapter we introduce the concept of regression from a machine learning point of view. We will present the fundamental regression method: linear regression. We will show how to fit a linear regression model and to make predictions from the model.

Exercise 1: Welcome and Introduction Exercise 2: Identify the regression tasks Exercise 3: Linear regression - the fundamental method Exercise 4: Code a simple one-variable regression Exercise 5: Examining a model Exercise 6: Predicting once you fit a model Exercise 7: Predicting from the unemployment model Exercise 8: Multivariate linear regression (Part 1)Exercise 9: Multivariate linear regression (Part 2)Exercise 10: Wrapping up linear regression

Now that we have learned how to fit basic linear regression models, we will learn how to evaluate how well our models perform. We will review evaluating a model graphically, and look at two basic metrics for regression models. We will also learn how to train a model that will perform well in the wild, not just on training data. Although we will demonstrate these techniques using linear regression, all these concepts apply to models fit with any regression algorithm.

Exercise 1: Evaluating a model graphically Exercise 2: Graphically evaluate the unemployment model Exercise 3: The gain curve to evaluate the unemployment model Exercise 4: Root Mean Squared Error (RMSE)Exercise 5: Calculate RMSE Exercise 6: R-squared Exercise 7: Calculate R-squared Exercise 8: Correlation and R-squared Exercise 9: Properly Training a Model Exercise 10: Generating a random test/train split Exercise 11: Train a model using test/train split Exercise 12: Evaluate a model using test/train split Exercise 13: Create a cross validation plan Exercise 14: Evaluate a modeling procedure using n-fold cross-validation

Before moving on to more sophisticated regression techniques, we will look at some other modeling issues: modeling with categorical inputs, interactions between variables, and when you might consider transforming inputs and outputs before modeling. While more sophisticated regression techniques manage some of these issues automatically, it's important to be aware of them, in order to understand which methods best handle various issues -- and which issues you must still manage yourself.

Exercise 1: Categorische invoervariabelen Exercise 2: De structuur van categorische input verkennen

Huidige oefening

Exercise 3: Modelleren met categorische inputs Exercise 4: Interacties Exercise 5: Een interactie modelleren Exercise 6: Een interactie modelleren (2)Exercise 7: De respons transformeren vóór het modelleren Exercise 8: Relatieve fout Exercise 9: Modeleren met log-getransformeerde monetaire output Exercise 10: RMSE vergelijken met root-mean-squared relatieve fout Exercise 11: Invoer transformeren vóór het modelleren Exercise 12: Inputtransformaties: de "hockeystick"Exercise 13: Inputtransformaties: de "hockeystick" (2)

Now that we have mastered linear models, we will begin to look at techniques for modeling situations that don't meet the assumptions of linearity. This includes predicting probabilities and frequencies (values bounded between 0 and 1); predicting counts (nonnegative integer values, and associated rates); and responses that have a non-linear but additive relationship to the inputs. These algorithms are variations on the standard linear model.

Exercise 1: Logistic regression to predict probabilities Exercise 2: Fit a model of sparrow survival probability Exercise 3: Predict sparrow survival Exercise 4: Poisson and quasipoisson regression to predict counts Exercise 5: Poisson or quasipoisson Exercise 6: Fit a model to predict bike rental counts Exercise 7: Predict bike rentals on new data Exercise 8: Visualize the bike rental predictions Exercise 9: GAM to learn non-linear transforms Exercise 10: Writing formulas for GAM models Exercise 11: Writing formulas for GAM models (2)Exercise 12: Model soybean growth with GAM Exercise 13: Predict with the soybean model on test data

In this chapter we will look at modeling algorithms that do not assume linearity or additivity, and that can learn limited types of interactions among input variables. These algorithms are *tree-based* methods that work by combining ensembles of *decision trees* that are learned from the training data.

Exercise 1: The intuition behind tree-based methods Exercise 2: Predicting with a decision tree Exercise 3: Random forests Exercise 4: Build a random forest model for bike rentals Exercise 5: Predict bike rentals with the random forest model Exercise 6: Visualize random forest bike model predictions Exercise 7: One-Hot-Encoding Categorical Variables Exercise 8: vtreat on a small example Exercise 9: Novel levels Exercise 10: vtreat the bike rental data Exercise 11: Gradient boosting machines Exercise 12: Find the right number of trees for a gradient boosting machine Exercise 13: Fit an xgboost bike rental model and predict Exercise 14: Evaluate the xgboost bike rental model Exercise 15: Visualize the xgboost bike rental model